linux-kernel - Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified range to map as encrypted

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Date:   Thu, 09 Mar 2023 15:45:35 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Borislav Petkov <bp@...en8.de>,
        Jörg Rödel <joro@...tes.org>,
        Usama Arif <usama.arif@...edance.com>
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
        "robh@...nel.org" <robh@...nel.org>, "kw@...ux.com" <kw@...ux.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "arnd@...db.de" <arnd@...db.de>, "hch@....de" <hch@....de>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
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        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "isaku.yamahata@...el.com" <isaku.yamahata@...el.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "jane.chu@...cle.com" <jane.chu@...cle.com>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>
Subject: Re: [PATCH v5 06/14] x86/ioremap: Support hypervisor specified
 range to map as encrypted

On Thu, 2023-03-09 at 15:45 +0100, Borislav Petkov wrote:
> On Thu, Mar 09, 2023 at 03:36:45PM +0100, Jörg Rödel wrote:
> > Yes, that is right. The key is mainly for the NMI entry path which can
> > be performance relevant in some situations. For SEV-ES some special
> > handling is needed there to re-enable NMIs and adjust the #VC stack in
> > case it was raised on the VC-handlers entry path.
> 
> So the performance argument is meh. That key will be replaced by
> 
>         if (cc_vendor == CC_VENDOR_AMD &&
>             cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)
> 
> which is something like 4 insns or so. Tops.
> 
> Haven't looked yet but it should be cheap.


cc_vendor isn't yet exposed. As we discussed this in IRC, I've been
updating the parallel bringup support for SEV-ES, including adding a
cc_get_vendor() function, in the top of my tree at
https://git.infradead.org/users/dwmw2/linux.git/commitdiff/parallel-6.2-v15
and it now looks like this:

	/*
	 * Encrypted guests other than SEV-ES (in the future) will need to
	 * implement an early way of finding the APIC ID, since they will
	 * presumably block direct CPUID too. Be kind to our future selves
	 * by warning here instead of just letting them break. Parallel
	 * startup doesn't have to be in the first round of enabling patches
	 * for any such technology.
	 */
	if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)) {
		switch (cc_get_vendor()) {
		case CC_VENDOR_AMD:
			has_sev_es = true;
			break;

		default:
			pr_info("Disabling parallel bringup due to guest state encryption\n");
			return false;
		}
	}

Using an explicit CC_ATTR_NO_EARLY_CPUID flag instead of
CC_ATTR_GUEST_STATE_ENCRYPT which is merely an approximation of that,
might be interesting.

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